The cellular phones of today have more and more different functions and applications in them. One such function is the possibility to make economical transactions. In performing transactions there is normally used security data in the form of private encryption keys. The storage of these keys has to be safe and safeguarded from manipulation.
In relation to cellular phones these keys have up till now been stored in so-called NOR flash memories. These known memories are of the type XIP (execute in place), which means that the keys are not moved from the memory. It is today possible to block writing of the position of such keys on such a memory using hardware solutions. Such solutions monitor program execution and data access on the system bus inside the phone. Software code that is not part of the authenticated firmware of the device is prevented from accessing the keys. These solutions assume that at least the firmware and possibly the keys are located in an XIP memory, so that address patterns on the bus are fixed for any given execution sequence.
Such NOR flash memories are however relatively expensive, why there is a trend to replace them with so-called NAND flash memories, which are cheaper. These memories are however not of the XIP type, and in order to use the content stored on them, the content has to be moved or copied to a working memory of the phone.
There is therefore a need for being able to protect such security data from manipulation when it is being moved from the NAND flash memory to the working memory.
It is furthermore often desirable to provide such a protection independently of the central processing of the unit, since otherwise other units such as a debugging unit, which is often a part of the phone for development reasons, can influence such security information.